Production of butadiene



PRODUCTION OF BUTADIENE Joseph R. Cobb, Jr., Bartlesville, Okla.,assignor to Phillips Petroleum Company, a corporation of Delaware FiledDec. 30, 1957, Ser. No. 706,050

3 Claims. (Cl. 26,0-4680) This invention relates to the production of1,3-butadiene. In one aspect, it relates to an improved process forproducing butadiene in increased yields. In another aspect it relates toa two-stage dehydrogenation of normal butane to butadiene and therecovery of the butadiene in substantially pure form.

A commercial process used in the production of 1,3- butadiene includesthe following steps: (l) butane dehydrogenation into butenes, (2) butenerecovery or purication, (3) butene dehydrogenation to butadiene, and (4)butadiene recovery or purification. In such a process, it isconventional to pass the eiuent from the step (1) dehydrogenation into abutene-1 fractionation column. The bottoms from this column containingprincipally normal butane and butene-2, after removal of any C5 andhigher hydrocarbons, are then introduced into an absorber wherein theyare contacted with a solvent which selectively dissolves the butene-2(step (2) purification). The dissolved butene-2, which is stripped fromthe rich solvent, is then employed with the butene-1 recovered asoverhead from the aforementioned butene-l column to form the feed forthe step (3) dehydrogenation. The undissolved fraction from theextractive distillation is passed into a fractional distillation columnfrom which a normal butane stream is taken overhead and then iiowed tothe step (l) dehydrogenation. The effluent from the step (3)dehydrogenation containing principally C4 and heavier hydrocarbons isthen subjected to fractional distillation in la butene-2 column so as torecover an overhead stream containing principally butadiene,isobutylene, butene-l and normal butane and a bottom stream containingprincipally normal butane, butene-2 and C5 hydrocarbons. The overheadstream from this latter fractional distillation is subjected toextractive distillation with a solvent selective for the butadiene whichis subsequently recovered from the solvent as product of the process(step (4) puriication). A portion of the undissolved fraction from theextractive distillation containing principally isobutylene, butene-1,normal butaneand butene-2 is recycled -to the step (3) dehydrogenationwhile another portion is vented or otherwise removed from the system.After removal of C5 and heavier hydrocarbons, one portion of the bottomslfrom the last-mentioned fractional distillation, i.e., the butene-2column, `is recycled to the step (3) dehydrogenation while a secondportion is recycled to the absorber used in the step (2) purification.

When operating in accordance with the above-described process the normalbutane takes a free ride through the step (3) dehydrogenation, acting asa diluent therein. In order to prevent overloading of the system, itbecomes necessary in normal operation to vent a portion of theundissolved fraction recovered from the absorber in the step (4)purication. It is also necessary to recycle a portion of the step (3)dehydrogenation lfeed recovered from the bottom of the butene-2 columnto the butene-1 column in order to prevent buildup of n-butane in thestep (3) dehydrogenation. V.It would be particularly desirable if amethod could be provided whereby the amount nite States Patent O ice offree-riding normal butane could be reduced while also obtaining moreeffective utilization of normal butane in the step (l) dehydrogenationand butene-1 in the step (3) dehydrogenation. This invention isconcerned with an improvement in the above-described process whichproduces this and other desirable results.

It is an object of this invention to provide an improved process forproducing butadiene from normal butane.

Another object of this invention is to provide a process for producingbutadiene wherein a large proportion of the normal butane whichconventionally takes a free ride through the butene dehydrogenation isconvertedV to butadiene.

A further object of the invention is to provide for a more eicientseparation of the materials obtained during the dehydrogenation ofn-butane to butene and during the dehydrogenation of butenes tobutadiene.

A still further object of the invention is to reduce the amount ofmaterial which must be purged during a twostage dehydrogenation ofn-butane.

Another object of the invention is to provide a process for thetwo-stage dehydrogenation of n-butane to butadiene in which a moreefficient utilization is made of the n-butane and butenes available forthe dehydrogenations.

Still another object of the invention is to provideV al process for thetwo-stage dehydrogenation of n-butane to butadiene in which it isunnecessary to recycle a portion of the step (3) dehydrogenation feed tothe step (2) puriiication,

Other objects and advantages of the invention Will become apparent tothose skilled in the art upon consideration of the accompanyingdisclosure and the drawing which shows schematically an arrangement ofapparatus and flow diagram according to the invention.

This invention is concerned with a process for the twostagedehydrogenation of normal butane to 1,3-butadiene. In one embodiment,the process comprises the following steps: catalytically dehydrogenatingnormal butane to normal butenes in the rst stage dehydrogenation zone,subjecting the C., hydrocarbon content of the first stagedehydrogenation eiuent to a first extractive distillation with a solventwhich is selective for butene-2, recovering an undissolved fractioncontaining butene-l and n-butane from the first extractive distillation,separating butene-1 from the undissolved fraction in a first fractionaldistillation zone and passing same to a second stage dehydrogenationzone, recovering a stream containing n-butane from the first fractionaldistillation zone and, after removal of C5 and heavier hydrocarbons,passing same into the first stage dehydrogenaton Zone, recovering astream containing butene-1, butene-2, butadiene and n-butane from theselective solvent and passing same into a second fractional distillationZone, catalytically dehydrogenating butenes supplied to the seconddehydrogenation zone to butadiene, recovering a second stagedehydrogenation eflluent consisting essentially of C4 and heavierhydrocarbons and passing same into the aforementioned second fractionaldistillation zone, recovering a rst stream containing principallybutene-2 from the second `fractional distillation zone and, afterremoval of C5 and heavier hydrocarbons, recycling same to the secondstage dehydrogenation zone, subjecting another stream recovered from thesecond fractional distillation zone to a second extractive distillationwith a solvent which is selective for butadiene, stripping the dissolvedfraction from the selective solvent and recovering from this fraction anessentially pure butadiene product, and passing the undissolved fractioncontaining principally butene-1, n-butane and isobutylene from thesecond extractive distillation to the first fractional distillationzone. A comparison of the process of this invention with the commercialprocess described hereinbefore indicates that there are severalimportant and distinct differences between the two processes. One of themost important differences between the two processes relates to theremoval of butene-1 from the rst stage dehydrogenation euent. In theabove-described commercial process,4 the butene-l is separated from theeffluent prior to the introduction of this latter stream into theextractive distillation column. In accordance with the process of theinstant invention, the feed to the butene-1 removal step consists ofthe, undissolved fractions from the extractiveA distillation steps.Operation in this manner makes it possible to effectively remove normalbutane from the second stage dehydrogenation and eliminate the step ofrecycling a portion of the second stage dehydrogenation feed.Furthermore, the process of this invention provides for a more effectiveutilization of the normal butane and butenes in the dehydrogenationsteps, thereby making it possible to increase the butadiene yield overthat conventionally obtained.

A better understanding of the invention can beobtained by referring tothe drawing which illustrate diagrammatically a preferred embodiment ofthe invention. In the apparatus as illustrated, various items ofequipment, such as valves, compressors, accumulators, heaters, and thelike, have been omitted in order to simplify the drawing; however theinclusion of such equipment can be readily accomplished by those skilledin the art.

Normal butane, obtained from natural gas or gasoline, or from any othersuitable source, is passed by means of line 10 into dehydrogenation zone11. Prior to introduction into zone 11, the normal butane isconventionally passed through a heater (not shown) wherein it ispreheated to a desired temperature. In dehydrogenation zone 11,approximately one third to one half of the butane is catalyticallyconverted to mixed butenes by dehydrogenation. A catalyst comprisingalumina and chromia, together with small amounts of beryllia ormagnesia, is prefer-red. However, any of the many parafn dehydrogenationcatalysts known in the art may be used. The precise conditions used inthe dehydrogenation depend upon the particular catalyst employed, itsactivity, and various other factors. However, a gas space velocity of500 to 1500 volume of butane per volume of catalyst per hour,temperatures in the range of 1000 to l200 F., and approximatelyatmospheric pressure, in general, constitute suitable conditions forconducting the first stage dehydrogenation.

The dehydrogenation effluent recovered from zone 11 through line 12 isthen passed into compressor system 13 where the reaction products arecompressed and cooled between stages in a conventional manner. Thedehydrogenation effluent contains principally hydrogen, butene-l,butene-2 (both low and high boiling) and normal butane. Small quantitiesof light gases other than hydrogen, e.g., methane, ethylene, ethane,propylene, and propane, are also produced in the reaction. Furthermore,small amounts of isobutane, isobutylene, and butadiene are present inthe dehydrogenation effluent stream. The effluent may also containhydrocarbons having or more carbon atoms, but the quantity of suchhydrocarbons is usually very small.

After passage -through compressor system 13, the hydrocarbon vapors arethen introduced via line 14 into a lean oil absorber and stripper unit.An overhead fraction containing C3 and lighter hydrocarbons is withdrawnfrom the lean oil absorber through line 16. The stripped hydrocarbonsare recovered through line 17 and then passed into fractionator 18 whichfunctions as a depropanizer to remove additional C3 and lighterhydrocarbons. The C3 and lighter hydrocarbons are withdrawn fromdepropanizer 18 as the overhead product through line 19. The kettleproduct from` depropanizer `18, which contains butene-.1, butene-,2,butadiene, n-butane and heavier hydrocarbons, is recovered through line21 and then passed into fractionator 22. Fractionator 22 operates as adeoiler, C5 and Vheavier hydrocarbons being withdrawn through line 23.The stream containing principally C4 hydrocarbons recovered as theoverhead product from deoiler 22 through line 24 is introduced intoeXtractive distillation column or absorber 26. In extractivedistillation column 26, the stream is contacted with a solvent whichselectively dissolves the butene-Zs. Although it is not intended tolimit the invention to any specific selective solvent, it is preferredto utilize furfural as the solvent. The solvent containing dissolvedbutene-2 is withdrawn from the bottom of absorber 26 through line 27 andthen passed into stripper 28. The stripped solvent recovered fromstripper 28 as the kettle product through line 29 is recycled toabsorber 26. A stream containing butene-2 is recovered as the overheadproduct from stripper 28 through line 31. The unabsorbed hydrocarbons,consisting principally of butene-1 and normal butane, are removed fromabsorber 26 through line 32 and then introduced into fractionaldistillation column 35. Since column 25 operates as a butene-l column, astream containing principally butene-l is recovered as the overheadproduct through line 34. The kettle product containing normal butanewhich is recovered from fractionator 35 through line I36 is passed intofractional distillation column 37. A stream containing principallynormal butane is recovered as the overhead product from column 37through line 38 while a stream containing heavier hydrocarbons and anysolvent carried over from stripper 28 is recovered as the kettle productthrough line 39. The overhead product stream from column 37 is recycledto dehydrogenation zone 11 `wherein the normal butane is converted tobutenes.

The overhead product streams recovered from stripper 28 and fractionator35 through lines 31 and 34, respectively, constitute the feed materialutilized in the second stage dehydrogenation. As shown in the drawing,the overhead stream from column 35 is passed directly into butenedehydrogenation zone 41. However, the overhead stream from stripper 28recovered through line 31 is further treated to remove normal butane andbutadiene prior to being used as a feed in the second stagedehydrogenation. Accordingly, line 31 from stripper 28 is furtherconnected to line 42 through which the feed to fractionator 43 ischarged. Since fractionator 43 functions as a butene-2 column, thekettle product recovered through line 44 contains principally butene-2.In order to remove C5 and heavier hydrocarbons, the kettle productrecovered from column 43 is passed into fractionator 46 which serves asa deoiler. rPhe C5 and heavier hydrocarbons are recovered from thedeoiler as the bottom product through line 47. The overhead fractionfrom deoiler `46 containing principally butene-2 is recovered throughline 48 and then passed into butene dehydrogenation zone 41.

In dehydrogenation zone 41, the butenes are catalytically dehydrogenatedto butadiene. While the catalyst used in zone 41 is preferably onecomprising about 93 percent Fe203, 5 percent Cr203 and 2 percent K2O, itis to be understood that other known olefin dehydrogenation catalystscan be used Without departing from the spirit or scope of the invention.Temperatures in the range of 1050 to 1350i F. are generally employed inthe second stage dehydrogenation while the pressure maintained in zone41 is preferably atmospheric or subatmospheric. The dehydrogenationeffluent from zone 41 consisting principally of butadiene, isobutylene,butene-1, normal butane, and butene-2 is passed through line 49 into acompressor system1`51. After passage through the compressor system, thecompressed effluent is introduced via line 52 into lean oil absorber andstripper unit 53. C3 and lighter hydrocarbons are withdrawn from thelean oil absorber through line 54 while C4 and heavier hydrocarbons arerecovered from the stripper through line 56 and then passed intofractionator 57. Additional C3 and lighter hydrocarbons are recoveredfrom fractionator 57, which functions as a depropanizer,

through line 58. The kettle product from; depropanizer 57 containingprincipally C4 and heavier hydrocarbons l tionator 43 through line 61contains principally 1,3-butadiene, butene-l, normal butane andisobutylene. Thereafter, this stream is passed intoextractivedistillation column or absorber 62 wherein it is contacted with asolvent which is selective for butadiene. While it is preferred toutilize furfural as a solvent, it is Vto be funderstood that othersolvents suitable for making the desired separation can be utilized. Therich solvent containing absorbed b-utadiene which is recovered fromabsorber 62 through line 63 is then passed' into stripper 64. Instripper 64, the hydrocarbons are stripped from the solvent,` beingremoved as an overhead product through line A66 and then passed intofractionator 67. Lean furfural absorbent is recovered from the bottom ofstripper 64 through line 68 and then recycled to absorber 62. Butadieneis recovered from fractionator 67 through line 69 as the product of theprocess while any heavier hydrocarbons and any solevnt or polymercarried over from the stripper are recovered las the kettle product fromcolumn 67 through line 71.

An undissolved fraction containing principally butenel, normal butaneand isobutylene is recovered from absorber 62 through -line 72; Aportion of this fraction is passed by means of line 73 into line 32through which feed to fractionator 35 is charged. Butene-l, contained inline 73 and introduced into column 35 through line 32 is recovered as Iaportion of the overhead product from column 35 through 34. The butene-lso recovered is subsequently recycled to butene dehydrogenation zone 41by means of line 34. Normal butane contained in line 73 is included inthe kettle product recovered from column 35 and subsequentlyrecovered asa portion of the overhead product from column 37. As previouslymentioned, the overhead product from column 37 is recycled todehydrogenation zone 11. Line 74 provides means for venting a part ofthe undissolved fraction recovered from absorber 62. However, the

that vented in a conventional process.

portion of theu'nabsorbed fraction recovered from ahsorber 62 isgenerally recycled to butene dehydrogenation zone 41. However,v becausesuch a conventional process provides no means for removing normal butaneYfrom the system, it is necessary to purge or vent a large i proportionof the stream recovered from the absorber in order to prevent the systemfrom becoming overloaded.

Y According to the instant invention, it is seen that means are providedwhereby the butene-l and normal butane contained in the overhead streamfrom absorber 62 ,are separated, the materials then being recycled tothe appropriate dehydrogenation steps. As a result, a more efficientutilization is made of the normal butane and Y been included in thematerial balance.

In a conventional process for producing butadiene, a

butene-1, thereby making possible a greater yield of butadiene from thatusually obtained.

A more comprehensive understanding of the invention can be obtained byreferring to the following illustrative examples which are not intended,however, to be unduly limitative of the invention.

EXAMPLE I A feed material containing normal butane is dehydrogenatedover an Al2O3-Or2O3-Mg0 catalyst at about 1100 F. and 24 p.s.i.g. Thedehydrogenationr eiiluent is then treated, as described hereinabove withrelation to the drawing, so as to separately recover normal butane andbutenes. The normal butane is recycled to the aforementioned normalbutane dehydrogenation step. The recovered butenes are dehydrogenatedover an Fe2O3--Cr2O3-K2O catalyst at about 1150 F. and 20 p.s.i.'g. Theeiuent from the butene dehydrogenation is then treated so as to recovera substantially pure butadiene product stream. As mentioned in thedescription of the drawing, an overhead fraction containing principallybutene-1, n-butane, and isobutylene is recovered from the furfuralabsorber during the treatment of the butene dehydrogenation eluent. This.fraction is further treated so as to separately recover n-butane andbutene-l which are then supplied to the butane and butenedehydrogenation steps as appropriate. The operating conditions for thevarious items of equipment are set forth hereinbelow in Table I whilethe amounts of materials in gallons per hour flowing in the variouslines are shown in Table II'. Hydrocarbons other than those listed, suchas acetylenes, may be present in the streams; however the amounts are sosmall that they have not The numerals used in the ltables correspond15o-reference numerals used in the drawing to designate lines or piecesof equipment.

EXAMPLE II A control run is made in which the same feed material as thatutilized in Example I is dehydrogenated in accordance with aconventional process. The catalysts and Table I Inlet Column ColumnColumn Column Temp., Top Bottom Iop Bottom F. Temp., Temp., Pressure,Pressure,

F. F. p.s.l.g. p.s.i.g

Lean Oil:

Absorber (15) 95 Stripper (15) 341 Depropanzer (18)-.-. 100 Deoller (22)196 Furfural:

Absorber (26)... 135 Stripper (28 298 Butene-l Column (35)-.. 110n-Butane-Golumn (37) 185 Lean Oil:

98 pp 360 Depropanizer (57) 149 Butene-2 Column 140 Deoller(46).---;.'..`.-' 168 Furtural: t

133 pper 283 Butadiene Column (67 85 Table Il Streamy Isobuty- Butene-lButan-Butane Butene-2 05's and Total lenes diene higher Feed to Deoller(17) 60 3, 040 590 26, 900 5, 900 375 36, 865 Deoiler Overhead (24) 603, 040 590 26, 860 5,890 235 36,675 Deoller Bottoms (23) 140 190Furfural Absorber Overhead (32)... 60 2,215 5 26, 740 140 200 29,360Furfural Stripper Overhead (31) 825 585 120 5, 750 35 7, 315 Butene-lC01.:

Recycle (73) 8, 195 85 380 160 10, 160

Feed (30) 10, 410 90 27, 120 300 200 29, 520

Overhead (34) 110 60 280 10 11, 860

Bittlzoms (36)--. 0 30 26, 840 290 200 27,660 11- 4 0 .I

Overhead (38) 300 30 26, 840 290 180 27, 640

Bottoms (39) 20 20 Butene Dehyd. Feed (48) plus (34). 1, 400 10, 180 1301,080 19,050 325 32, 165 Butene Dehyd. Elueut (49) 1, 400 7,840 5,0001,080 13,625 615 29, 560 Butene-2 Col.:

Feed (42) 1, 400 8, 665 5, 585 1, 200 19, 375 650 36, 875

Overhead (61) 1,400 8,595 5, 515 400 300 16,210

Bottoms (4 70 70 800 19,075 650 20,665 Deoiler Overhead (48) 70 70 80019, 040 325 20, 305 Deoiler Bottoms (47).- 35 325 360 Furfural AbsorberOverhead (72) l, 400 8, 565 400 170 10, 625 Purge (74) 60 370 5 20 10465 Furfural Stripper Overhead (66) 30 5, 425 130 5, 585 Butadiene Col.Overhead (Product) (70) 5,415 60 5,475

Butadiene O01. Bottoms (71) 10 70 80 the dehydrogenation conditions arethe same as those used in the run described in Example I. In the controlrun, the effluent from the n-butane dehydrogenation, after removal of C3and lighter hydrocarbons in a depropanizer, is passed into a butene-lcolumn prior to being treated in the furfural absorber. (It is notedthat in the run of Example I the butene-l column is positioned after thefurfural absorber and stripper.) The overhead from the butene-l columnis passed to a butene-Z column, the bottoms of this latter columnserving as a portion of the butene dehydrogenation feed after removal ofC and heavier hydrocarbons in a deoiler. A part of this feed portion isrecycled to the -furfural absorber used in the butene-2 separation.(This is eliminated in the instant process.) The bottoms from thebutene-l column, after removal of C5 and heavier hydrocarbons in adeoiler, are passed into a furfural absorber. The unabsorbed overheadfraction from the furfural absorber is charged 25 to a n-butane columnwhose overhead is recycled to the butane dehydrogenation zone. The richsolvent recovered from the bottom of the furfural absorber is passedinto a stripper, the overhead from which is used as a portion of thefeed in the butene dehydrogenation. The overhead from the butene-2column is charged to a furfural absorber for separation of the butadienein this stream. A portion of the unabsorbed overhead Ifraction from thefurfural absorber is recycled to the butene dehydrogenation step whileanother portion is vented. The bottoms of the furfural absorber ispassed into a stripper, the overhead from which is treated in abutadiene column for the recovery of the butadiene product. 'Ihe variouscolumns used in this run are operated at substantially the sameconditions as the corresponding columns employed in the run of ExampleI. The amounts of material in gallons per hour ilowing in the variousstreams are shown in Table III hereinbelow.

Table III Stream Isobutyl- Butene-l Butan-Butane Butene-Z 05's and Totaleues diene higher Feed to Butene-l Column 3, 040 590 26, 900 5,900 37536, 865 Butene-l Col. Overhead (Part of feed to Butene-2 Col.) 60 2, 760390 280 30 3, 520 Butene-l C01. Bottoms (Feed to Deoiler) 280 200 26,620 6, 870 375 33, 345 Deoiler Bottoms 40 10 140 190 Deoiler Overhead(Part of feed to Furfural Absorber) 280 200 26, 580 5, 860 235 33, 155Recycle from deoiled Butene-2 Col.

bottoms (To Furfural Absorber). 10 10 220 1, 330 20 1, 590 FurfuralAbsorber Feed (Deoiler Overhead plus Recycle) 290 210 26, 800 7, 190 25534, 745 Furfural Stripper Overhead (Butene Dehyd. Feed) 240 205 1207,050 40 7, 655 Furfur Absorber Overhead (Feed to n-Butane 001.)- 50 526, 680 140 215 27, 090 n-Butane Col. Overhead (To Butane Dehyd.) 50 526, 680 140 195 27,070 n-Butaue Col. Bottoms- 20 20 Butene Dehyd. Feed540 8, 290 340 3, 320 19,015 350 31,855 Bntene Dehyd. Emuent 540 6,1604, 970 3, 320 13, 500 640 29,130 Butene-2 Col. Feed (Butene-l Col.

Overhead plus Ediuent) 600 8, 920 5, 360 3, 600 13, 530 640 32, 650Butene-2 Col. Overhead (Feed to Furfural Absorber) 600 8, 850 5, 290 1,400 300 16, 440 Butene2 Col. Bottoms (Feed to Deoiler) 70 2,200 13, 230640 16, 210 Deoiler Overhead- 70 70 2, 160 13, 195 330 15, 825 DeoilerBottoms 40 35 310 385 Deoiler Overhead less Recycle (Butene Dehyd. Feed)60 60 1, 940 11,865 310 14, 235 Furfural Absorber Overhead 600 8, 820 851, 400 170 11, 075 Purge 60 880 10 140 20 1, 110 Recycle to ButeneDehyd.

Abs. Overhead'less Purge) Y 540 7, 940 150 9, 965 Furural StripperOverhead (B adiene Gol. Feed). Y 30 5,365 Butadiene Col. Overhead(Product) 30 5, 285 Butadiene Col. Bottoms A comparison of the data setforth in Tables II and III shows the advantages obtained by proceedingin accordance with the process of this invention. Thus, it is seen thatonly 465 gallons of material per hour are purged in the instant processas compared with 1110 gallons per hour in the control run. As a result,additional n-butane and butene-l are made available from which butadienecan be produced. In this regard, it is noted that in the run of ExampleI 5415 gallons of butadiene per hour are obtained as compared with ayield of 5195 gallons per hour in the control run of Example II.Operation in accordance with the instant process provides for theeffective removal of n-butane, thereby greatly reducing the amount ofthis material recycling within the system. Furthermore, it is possibleto eliminate the recycle of the deoiled bottoms from the butene-2 columnto the furfural absorber used in the butene purification.

As Will be evident to those skilled in the art, many variations andmodifications of the invention can be practiced in View of the foregoingdisclosure. Such variations and modifications are believed to be clearlywithin the spirit and scope of the invention.

I claim:

1. A process for the production of 1,3-butadiene which comprisescatalytically dehydrogenating normal butane to normal butenes in a rststage dehydrogenation zone; subjecting the C4 hydrocarbon content of theeluent from said first stage dehydrogenation zone to a first extractivedistillation with a solvent selective for butene-2; recovering anundissolved fraction containing butene-1 and nbutane from said firstextractive distillation; separating butene-1 from said undissolvedfraction in a first fractional distillation zone; passing said butene-1to a second stage dehydrogenation zone; recovering a stream containingn-butane from said first fractional distillation zone; separating C5 andheavier hydrocarbons Ifrom said n-butane stream of said first fractionaldistillation zone; recycling the resulting n-butane-containing streamsto said rst stage dehydrogenation zone; recovering solvent containingdissolved C4 hydrocarbons from said first extractive distillation;stripping a stream containing butene-l, butene-2, butadiene and n-butanefrom said solvent; passing said latter stream of butene-l, butene-2,butadiene and n-butane into a second fractional distillation zone;catalytically dehydrogenating butenes supplied to said second stagedehydrogenation zone; recovering an effluent containing C4 and heavierhydrocarbons from said second stage dehydrogenation zone; passing saideliiuent into said second lfractional distillation zone; recovering astream containing butene-2 from said second fractional distillationzone; separating `C5 and heavier hydrocarbons from said butene-2 streamof said second fractional distillation zone; recycling the resultingbutene-Z-containing stream to said second stage dehydrogenation zone,recovering a stream containing butadiene, butene-l, n-butane andisobutylene from said second fractional distillation zone; subjectingsaid butadiene, butene-1, n-butane and isobutylene stream to a secondextractive distillation with a solvent selective for butadiene;recovering an undissolved fraction containing butene-1, n-butane andisobutylene from said second extractive distillation; passing saidundissolved fraction into said first fractional distillation zone;recovering solvent containing dissolved butadiene from said secondextractive distillation; and separating butadiene from said solvent asthe product of the process.

2. The process according to claim 1 wherein said selec-i tive solvent isfurfural.

3. A process for production of 1,3-butadiene which`= comprisescatalytically dehydrogenating n-butane to n butene in a first stagedehydrogenation zone; compressing the efiiuent gases from said firststage dehydrogenation zone; separating C3 and lighter hydrocarbons fromsaid compressed efliuent gases in a first absorption zone and a firstdepropanizing zone respectively; passing a product stream containing C4and heavier hydrocarbons from said first depropanizing zone to a firstdeoiling zone; separating C5 and heavier hydrocarbons from said productstream in said first deoiling zone; subjecting said product streamcontaining C4 hydrocarbons to a first extractive disillation with asolvent selective for butene-2; recovering an undissolved fractioncontaining butene-l and n-butane from said second extractivedistillation; separating butenel from said undissolved fraction in afirst fractional distillation zone; passing said butene-1 to a secondstage dehydrogenation zone; recovering a stream containing nbutane fromsaid first fractional distillation zone; separating C5 and heavierhydrocarbon from said n-butane of said first fractional distillationzone; recycling the resulting n-butane containing stream to said firststage dehydrogenation zone; recovering solvent containing dissolved C4hydrocarbons from said first extractive distillation; stripping a streamcontaining butene-1, butene-2, butadiene and n-butane from said solvent;passing said latter stream of butene-l, butene-2, butadiene and nbutaneinto a second fractional distillation zone; catalyticallydehydrogenating butene supplied to second stage dehydrogenation Zone;recovering an efiiuent containing C4 and heavier hydrocarbons from saidsecond stage dehydrogenation zone; compressing the effluent gases fromsaid second stage dehydrogenation zone; separating C3 and lighterhydrocarbons from said compressed effluent gases in a second absorptionZone and a second depropanizing zone respectively; passing a C4 andheavier hydrocarbon stream from said seco-nd depropanizing zone intosaid second fractional distillation zone; recovering a stream containingbutene-2 from said second fractional distillation Zone; separating C5and heavier hydrocarbons from said butene-2 stream of said secondfractional distillation zone in a second deoiling zone; recycling theresulting butene-2 containing stream to said second stagedehydrogenation Zone; recovering a stream containing butadiene,butene-1, n-butane and isobutylene from said second fractionaldistillation zone; subjecting said butadiene, butene-l, n-butane andisobutylene stream to a second extractive distillation With a solventselective -for butadiene; recovering an undissolved fraction containingbutene-l, n-butane and isobutylene from said second extractivedistillation; passing said undissolved fraction into said firstfractional distillation zone; recovering solvent containing dissolvedbutadiene from said second extractive distillation; and separatingbutadiene from said solvent as a product of the process.

References Cited in the file of this patent UNITED STATES PATENTS2,209,215 Gaylor et al July 23, 1940 2,379,332 Arnold June 26, 19452,386,310 Hachmuth Oct. 9, 1945 2,395,016 Schulze et al Feb. 19, 19462,554,054 Owen May 22, 1951 2,750,435 Fetchin June 12, 1956

1. A PROCESS FOR THE PRODUCTION OF 1,3-BUTADIENE WHICH COMPRISESCATALYTICALLY DEHYDROGENATING NORMAL BUTANE TO NORMAL BUTENES IN A FIRSTSTAGE DEHYDROGENATION ZONE, SUBJECTING THE C4 HYDROCARBON CONTENT OF THEEFFLUENT FROM SAID FIRST STAGE DEHYDROGENATION ZONE TO A FIRSTEXTRACTIVE DISTILLATION WITH A SOLVENT SELECTIVE FOR BUTENE-2,RECOVERING AN UNDISSOLVED FRACTION CONTAINING BUTENE-1 AND NBUTANE FROMSAID FIRST EXTRACTIVE DISTILLATION, SEPARATING BUTENE-1 FROM SAIDUNDISSOLVED FRACTION IN A FIRST FRACTIONAL DISTILLATION ZONE, PASSINGSAID BUTENE-1 TO A SECOND STAGE DEHYDROGENATION ZONE, RECOVERING ASTREAM CONTAINING N-BUTANE FROM SAID FIRST FRACTIONAL DISTILLATION ZONE,SEPARATING C5 AND HEAVIER HYDROCARBONS FROM SAID N-BUTANE STREAM OF SAIDFIRST FRACTIONAL DISTILLATION ZONE, RECYCLING THE RESULTINGN-BUTANE-CONTAINING STREAMS TO SAID FIRST STAGE DEHYDROGENATION ZONE,RECOVERING SOLVENT CONTAINING DISSOLVED C4 HYDROCARBONS FROM SAID FIRSTEXTRACTIVE DISTILLATION? STRIPPING A STREAM CONTAINING BUTENE-1,BUTENE-2, BUTADIENE AND N-BUTANE FROM SAID SOLVENT, PASSING SAID LATTERSTREAM OF BUTENE-1, BUTENE-2, BUTADIENE AND N-BUTANE INTO A SECONDFRACTIONAL DISTILLATION ZONE, CATALYTICALLY DEHYDROGENATING BUTENESSUPPLIED TO SAID SECOND STAGE DEHYDROGENATION ZONE, RECOVERING ANEFFLUENT CONTAINING C4 AND HEAVIER HYDROCARBONS FROM SAID SECOND STAGEDEHYDROGENATION ZONE, PASSING SAID EFFLUENT INTO SAID SECOND FRACTIONALDISTILLATION ZONE, RECOVERING A STREAM CONTAINING BUTENE-2 FROM SAIDSECOND FRACTIONAL DISTILLATION ZONE, SEPARATING C5 AND HEAVIERHYDROCARBONS FROM SAID BUTENE-2 STREAM OF SAID SECOND FRACTIONALDISTILLATION ZONE, RECYCLING THE RESULTING BUTENE-2-CONTAINING STREAM TOSAID SECOND STAGE DEHYDROGENATION ZONE, RECOVERING A STREAM CONTAININGBUTADIENE, BUTENE-1, N-BUTANE AND ISOBUTYLENE FROM SAID SECONDFRACTIONAL DISTILLATION ZONE, SUBJECTING SAID BUTADIENE, BUTENE-1,N-BUTANE AND ISOBUTYLENE STREAM TO A SECOND EXTRACTIVE DISTILLATION WITHA SOLVENT SELECTIVE FOR BUTADIENE, RECOVERING AN UNDISSOLVED FRACTIONCONTAINING BUTENE-1, N-BUTANE AND ISOBUTYLENE FROM SAID SECONDEXTRACTIVE DISTILLATION, PASSING SAID UNDISSOLVED FRACTION INTO SAIDFIRST FRACTIONAL DISTILLATION ZONE, RECOVERING SOLVENT CONTAININGDISSOLVED BUTADIENE FROM SAID SECOND EXTRACTIVE DISTILLATION, ANDSEPARATING BUTADIENE FROM SAID SOLVENT AS THE PRODUCT OF THE PROCESS.